Certain lighting applications benefit from use of flexible lighting devices such as rope lights. Flexible lighting devices may be used in interior and exterior environments and can be used for sign applications. One benefit of flexible lighting devices is that they can be used to conform to contours of objects or structures, and they may be used to generate various shapes and text.
Neon lamps, fluorescent lamps, and incandescent lamps have been widely used in the sign industry for many years. Such lamps suffer from limitations that restrict their utility. For example, neon and fluorescent lights may be difficult to start in cold weather, typically require high operating voltages, and may include hazardous materials (e.g., mercury) that pose environmental and disposal risks. Incandescent lamps are characterized by short lamp life, low luminous efficiency, and poor resistance to vibration.
Light emitting diode (LED) lamps present a desirable alternative to the foregoing technologies, to provide benefits such as improved efficiency, extended operating life, improved resistance to vibration, and capability to operate with variety of voltages. Light emitting diodes (LEDs) are solid state devices that convert electric energy to light, and generally include one or more active layers of semiconductor material sandwiched between oppositely doped layers. When bias is applied across doped layers, holes and electrons are injected into one or more active layers where they recombine to generate light that is emitted from the device. Laser diodes are solid state emitters that operate according to similar principles.
Individual solid state emitters typically embody relatively narrow spectral output. Individual solid state emitters can emit discrete colors such as red (R), green (G), blue (B), yellow (Y), cyan (C), or other colors of light. Solid state light sources may also be utilized to provide white light (e.g., perceived as being white or near-white), and have been investigated as potential replacements for conventional white incandescent and/or fluorescent lamps. Light perceived as white or near-white may be generated by a combination of multiple discrete color emitters (e.g., red, green, and blue (“RGB”) LED emitters), or, alternatively, by combined emissions of a blue LED and a yellow phosphor. In the latter case, a portion of the blue LED emissions pass through the phosphor, while another portion of the blue LED emissions is ‘downconverted’ to yellow; the combination of blue and yellow light provide a white light. Another approach for producing white light is to stimulate phosphors or dyes of multiple colors with a violet or ultraviolet LED source.
Many modern lighting applications require high power solid state emitters to provide a desired level of brightness. High power solid state emitters can draw large currents, thereby generating significant amounts of heat that must be dissipated.
LED rope lights including LEDs contained within an elongated, flexible light-transmissive tube (e.g., such as embodied in U.S. Pat. No. 6,406,166 to Ko and U.S. Pat. No. 7,210,818 to Luk et al) are known. Rope lights of such conventional type have limited means for dissipating heat. U.S. Pat. No. 6,406,166 makes no mention at all of heat transfer. U.S. Pat. No. 7,210,818 discloses use of a wire stiffening member embedded in a helical (spiral shaped) circuit board supporting numerous LEDs within a flexible tube, with the stiffening member acting as a heatsink to draw heat generated by LEDs through associated electrical leads of the LEDs; however, heat generated by the LEDs remains trapped within the tube. This limits the ability to drive the rope light at high operating currents without causing the LEDs to overheat, leading to shortened operating life.
Although not explicitly directed to rope lights, U.S. Pat. No. 6,762,562 to Leong discloses use of a tubular housing containing LEDs therein, such as on a generally cylindrical circuit board or multiple spaced-apart rigid support structures disposed within the housing. Heatsinks and internal vent holes arranged within the tubular housing may be used to conduct heat generated by LEDs, with the heat being dissipated through ends of the tubular housing. Such arrangement limits the ability to provide a lighting device of extended lengths and to drive such a device with high operating currents due to thermal stratification. That is, it may be difficult to transport heat from LEDs located far from ends of the device for dissipating through the ends, thereby raising the risk of LED failure or reduced operating life. Such arrangement may also limit the ability to connect multiple lighting devices in series, and requires that ends of the device embody adequate heat dissipating capability.
It would be desirable to provide flexible solid state lighting devices capable of withstanding at high operating currents without leading to shortened emitter operating life.
Conventional rope lights generally include from two to five lengthwise conductors, with two conductors permitting all lamps in a string to be controlled together, and with a greater number of conductors permitting different operating modes such as sequential operation of selected groups of lamps (e.g., providing chasing effects or alternating color illumination if multiple colors of emitters are provided). While it would technically be possible to provide an elongated flexible lighting device (e.g., rope light) with individual control of every emitter contained therein, implementation of such a concept is not practically feasible since providing at least one dedicated conductor for each lamp would render the resulting product unduly costly and bulky (e.g., large in diameter). It would be desirable to enhance the ability to control individual emitters or groups of emitters within a lighting device (e.g., an elongated lighting device) without unduly increasing the cost and bulk of the resulting product. It would further be desirable for such a product to be capable of withstanding at high operating currents without leading to shortened emitter operating life.
It would also be desirable to provide flexible arrays of solid state emitters capable of withstanding at high operating currents without leading to shortened emitter operating life. Such arrays of emitters would desirably be easily fabricated, configured, and controlled.
It would be desirable to provide flexible solid state lighting devices capable of reducing some or all of the limitations inherent to conventional flexible lighting devices.